The present invention relates to a keyboard and, more particularly, to a keyboard for reducing the power consumption thereof when transmitting key codes therefrom and, at the same time, enhancing the reliability in the key code transmission.
Generally, a keyboard is used as connected to a signal processing unit such as a personal computer by cable and has a key matrix with many keys laid out, an input/output circuit for performing input/output operations with the key matrix, a controller for controlling the entire operation of the keyboard, a clock signal generator for forming a clock signal for obtaining a scan signal, a display device for indicating a key-operated state and so on, an interface circuit for providing interface between the keyboard and the signal processor, and a built-in power supply.
FIG. 4 shows a block diagram illustrating an example of the constitution of a known keyboard.
Referring to FIG. 4, a keyboard 40 comprises a key matrix 41 with many keys laid out, an input/output (I/O) circuit 42 for receiving data associated with key operations from the key matrix 41, a controller (CPU) 43 for controlling the entire operation of the keyboard 40, an interface (I/F) circuit 44 for providing interface between the keyboard 40 and the signal processor (not shown) such as a personal computer, a clock signal generator 45 for forming a clock signal for obtaining a signal for scanning the key matrix 41, a ROM 46 for storing a program for operating the controller 43, a RAM 47 for use in the data processing by the controller 43, a display device (IND)48 for indicating a key-operated state and so on, a cable 49 for connecting the interface circuit 44 to the signal processor, and a built-in power supply 50.
In the above-mentioned prior-art constitution, the controller 43 performs various operations as follows. First, the controller 43 generates a scan signal for sequentially scanning horizontally and vertically the keys arranged on the keyboard. Second, the controller 43 receives switch data corresponding to an operated key when the keys have been scanned. Third, the controller 43 converts the received switch data to a key code (or a keyboard code) to be transmitted to the signal processor. Fourth, the controller 43 transmits the switch code to the signal processor via the interface circuit 44 and the cable 49. Fifth, the controller 43 transmits required display data to the display device 48. Sixth, the controller 43 executes required signal processing in response to command data supplied from the signal processor via the cable 49.
The keyboard 40 having the above-mentioned constitution operates as follows in general.
When any of the keys arranged on the key matrix 41 are operated, the controller 43 sequentially receives the switch data corresponding to the operated keys via the input/output circuit 42. Then, the controller 43, based on the operating program stored in the ROM 46, converts the switch data to key codes by use of the RAM 47 and transmits sequentially the obtained key codes to the signal processor via the interface circuit 44 and the cable 49. If, during or immediately before or after this transmission, some command data is supplied from the signal processor to the controller 43, the controller 43 performs a control operation corresponding to that command data.
FIG. 5 shows a timing chart describing the transmission timing of codes to be transmitted from the keyboard 40 when the Shift key and one operation key are operated simultaneously.
As shown in FIG. 5, in the keyboard 40 of FIG. 4, if one of the operation keys, for example key "A", is operated continuously (between time t.sub.1 and time t.sub.3) with the Shift key, one of the function keys, operated (between time to and time t.sub.4), a shift-on code indicating a key-on operation of the Shift key is transmitted at time t.sub.0, a key-on code A indicating a key-on operation of the key "A" is transmitted at time t.sub.1, key-on repeat codes A of the operation key "A" are sequentially transmitted at times t.sub.2(1), t.sub.2(2), . . . , t.sub.2(N), a key-off code A indicating a key-off operation of the operation key "A" is transmitted at time t.sub.3, and a shift-off code indicating a key-off operation of the Shift key is transmitted at time t.sub.4.
The above-mentioned operation holds true with other function keys such as Control and Alt keys.
In the known keyboard 40, if one of the operation keys, the key "AA" for example, is operated continuously (key on), the key-on repeat codes A are sequentially transmitted at short time intervals while the operation key "A" is being operated after the key-on code A is transmitted at the start of the key operation, and the key-off code A is transmitted at the end of the key operation as shown in FIG. 5, thereby terminating the transmission of a series of data for the operation of the operation key "A".
Also, in the known keyboard 40, if the Shift key, one of the function keys, is held operated (key on) at the time of the continuous operation of the operation key "A" for example, a shift-on code is transmitted at starting the operation of the Shift key as shown in FIG. 5 and a shift-off code is transmitted at the end of the Shift key operation, in addition to the above-mentioned data transmission.
As described, in the known keyboard 40, when an operation key is operated continuously, key-on repeat codes are transmitted, so that the power consumed for this transmission amounts to a degree that is not negligible. Especially, when the keyboard is driven by its built-in power supply, the power consumption by the transmission of key-on repeat codes shortens the service life of the power supply.
Further, in the known keyboard 40, if a function key such as the Shift key is operated immediately before an operation key is operated, the timing of transmitting the shift-on code at starting Shift key operation differs from the timing of transmitting the key-on code and the key-off code generated by the operation of the operation key, making it possible to fail the transmission of the shift-on code.
Still further, in the known keyboard 40, wireless transmission such as optical transmission is affected by noise and so on more than cable transmission, thereby lowering the reliability in code transmission.